1. Field of the Invention
The present invention relates to an electro-photographic photoreceptor containing an enamine compound capable of efficiently preventing image defects caused by oxidizing gas such as ozone and NOx, to an image formation apparatus provided with the electro-photographic photoreceptor, to an enamine compound and to a method for producing the enamine compound.
2. Description of the Related Art
Many electrophotographic system image formation apparatus (hereinafter also referred to as “electrophotographic device”) utilizing electrophotographic technologies to form an image are used for copying machines, printers, facsimile machines and the like.
In electrophotographic devices, an image is formed through an electrophotographic process mentioned below. First, the photosensitive layer of the electrophotographic photoreceptor (hereinafter also called “photoreceptor”) provided in the devices is charged and then exposed to light to form an electrostatic latent image. The formed electrostatic latent image is developed to form a toner image. Then, the formed toner image is transferred and fixed to a transfer receiving material such as recording paper to form a desired image on the transfer receiving material.
The electrophotographic technologies are currently utilized not only in the fields of copying machines but also in the fields of printing precursors, slide films, microfilms and the like, in which silver salt photo technologies have been conventionally utilized. These technologies are also applied to high-speed printers using, as its light source, a laser, light emitting diode (abbreviation: LED), cathode ray tube (abbreviation: CRT) and the like. Along with a spread of the range of applications of electrophotographic technologies, the requirements in the photoreceptors are becoming highly advanced and widely spread.
As the photoreceptor, widely used are inorganic photoreceptors which are provided with a photosensitive layer containing, as its major component, inorganic photoconductive materials such as selen, zinc oxide or cadmium sulfide.
The inorganic photoreceptor has fundamental characteristics required of photoreceptors to some extent. However, the inorganic photoreceptor has the drawback such that it has a difficulty in forming a film of the photosensitive layer, is deteriorated in plasticity and has high production cost. Also, the inorganic photoconductive materials are highly toxic in usual and are therefore largely limited in its production and handling.
As mentioned above, since these inorganic photoconductive materials and inorganic photoreceptors using these inorganic photoconductive materials have many drawbacks, the progress of research and development of organic photoconductive materials have been made.
In recent years, the organic photoconductive materials have been widely studied and developed. The organic photoconductive materials not only are utilized for electrostatic recording devices but also have become used in applications of sensor devices, organic electro luminescent (abbreviation: EL) devices and the like.
The organic photoreceptor using the organic photoconductive material have the advantage that the photosensitive layer is well formed as a film, is superior in flexibility, is light-weighted and has high transparency and therefore, a photoreceptor having high sensitivity for light in a wide wavelength range by an appropriate sensitizing method can be easily designed. Therefore, the organic photoreceptors are being developed as a leading photoreceptor day by day.
Though the organic photoreceptors have the drawbacks that they are deteriorated in sensitivity and durability in the early stages, these drawbacks have been significantly improved by the development of function separating type photoreceptors in which the charge generation function and charge transport function are shared by separate materials. Moreover, this function separating type photoreceptor has the advantage that the material constituting the photosensitive layer can be selected from a wide range of materials, so that photoreceptors having desired characteristics can be manufactured relatively easily in addition to the above advantage specific to the organic photoreceptors.
As the structure of such an organic photoreceptor, various structures have been proposed, these structures including a single layer structure in which a charge generation material and a charge transport material (also called “charge transport material” are both dispersed in a binder, which is then applied to a support and a laminate structure or reverse double layer type structure in which a charge generation layer obtained by dispersing a charge generation material in a binder and a charge transport layer obtained by dispersing a charge transport material in a binder resin are formed in this order or reverse order on a support. Among these structures, a functional separation type photoreceptor in which a charge transport layer is laminated on a charge generation layer is superior in electrophotographic characteristics and durability. Therefore, the photoreceptor characteristics can be variously designed due to its high degree of freedom of material selection, and are hence widely put to practical use.
As the charge generation material to be used in these function separation type photoreceptors, studies have been made as to various materials such as a phthalocyanine pigment, squalilium dye, azo pigment, perylene pigment, polycyclic quinine pigment, cyanine dye, squalenic acid dye and pyrylium salt type dye, and a variety of materials having high light fastness and high charge generation ability have been proposed.
Also, as the charge transport material, various compounds are known which include pyrazoline compounds, hydrazone compounds, triphenylamine compounds, stilbene compounds and enamine compounds.
Various performances such as a high-speed operation, durability and sensitive stability are demanded of photoreceptors having the structures that have been proposed or investigated. With regard to the characteristics of the photoreceptor, high sensitization that copes with a high-speed operation and an improvement in durability (=long life) which is made by an improvement in abrasive resistance and sensitive stabilization are required at the same time corresponding to a reverse developing system electrophotographic device such as a laser printer. In addition, higher image reliability and stability in repeated use are required of photoreceptors such as a laser printer.
However, it has been regarded as one large drawback of these photoreceptors that these photoreceptors are generally more deteriorated in durability than inorganic type photoreceptors. The durability is roughly divided into a kind of durability of photographic properties such as sensitivity, residual potential, charge ability and image fogs, and mechanical durability of, for example, abrasion and scratches of the surface of the photoreceptor caused by friction. The primary cause of a deterioration in durability of the photographic properties are known to be ozone, NOx (nitrogen oxides) and a deterioration caused by irradiation with light in a charge transport material contained in the surface layer of the photoreceptor. In the current circumstance, many charge transport materials constituted of various skeletons and proposed variously are not said to be satisfactory though improved in durability.
Also, the photoreceptor is repeatedly used in a system. In the system, it is required for the photoreceptor to always exhibit constantly stable photographic characteristics. In the current circumstance, as to such stability and durability, no structure satisfied in these properties has not been obtained yet so far.
Specifically, the repeated use of the photoreceptor causes a reduction in potential, a rise in residual potential and a change in sensitivity, bringing about a deterioration in the quality of copies, with the result that the photoreceptor cannot stand to use. Though all of the causes of the deterioration are not clarified, some causes are considered.
It has been clarified that oxidizing gases, for example, ozone and nitrogen oxide and the like emitted from a corona discharge/charge device give remarkable damages to the photosensitive layer. These oxidizing gases chemically change materials in the photoreceptor to bring about various characteristic changes. These oxidizing gases bring about, for example, a reduction in charge potential, rise in residual potential and reduction in resolution caused by a reduction in surface resistance, with the result that image fogs such as white voids and black bands occur on an output image, which deteriorate the image quality significantly and hence shortens the life of the photoreceptor. For such a phenomenon, there have been made a proposal including such ideas that gas around the corona charger is efficiently exhausted and replaced to avoid direct influence of the gas on the photoreceptor and a proposal in which an antioxidant and a stabilizer are added to the photosensitive layer to prevent the deterioration of the photoreceptor.
For example, it is disclosed in the publication of Japanese Unexamined Patent Publication No. SHO 62-105151 that an antioxidant having a triazine ring and a hindered phenol skeleton is added to a photosensitive layer and it is also disclosed in the publication of Japanese Unexamined Patent Publication No. SHO 63-18355 that a specific hindered amine is added to a photosensitive layer. It is also disclosed in each publication of Japanese Unexamined Patent Publication Nos. SHO 63-4238, SHO 63-216055 and HEI 3-172852 that a trialkylamine and an aromatic amine are added to a photosensitive layer. It is also disclosed in the publication of Japanese Unexamined Patent Publication No. HEI 5-158258 that an amine dimer is added in a photosensitive layer. However, these measures are still unsatisfactory.